Auxiliary power units in the form of small gas turbines may be provided for various combinations of shaft power output and compressed air output. Typically, they are of either the so-called "integral bleed" or "load compressor" type.
Extraction of compressor discharge air in the integral bleed auxiliary power units without concurrent shaftpower output (zero concurrent shaftpower output) plus requirements to operate in a 100% shaftpower mode only (zero bleed air output), result in performance compromises necessary to maintain adequate margin against compressor surge.
Variable turbine nozzles have been used to avoid the compromises by allowing the turbine to match optimum compressor efficiencies. Heretofore, in the case of radial inflow turbines, radial turbine nozzles have been utilized. An example of this type of machine is illustrated in a report entitled,"Interim report AFFDL-TR-77-68, Volume I" for period May 1976-July 1976, obtainable from the Air Force Flight Dynamic Laboratory (FED), Wright-Patterson Air Force Base, Oh., 45433, pages 86-95 thereof dealing with variable nozzle geometry.
While such geometry is of assistance in overcoming the performance compromises mentioned above, another difficulty exists. Specifically, the components of the variable nozzles when applied to a radial inflow turbine are operating in a relatively hot environment. Both the nozzle vanes and the actuating mechanism therefore is subjected to the heat with the consequence that power plant life and reliability may be lessened.
The present invention is directed to overcoming the foregoing problems.